The present invention relates to a solvent-free curable adhesive composition and a process of lamination with use of the adhesive composition. In further detail, the present invention relates to a solvent-free two-component curable adhesive composition for lamination useful in producing materials for packaging food, necessaries of life, and others, and to a process of lamination.
Currently, composite laminated films have been widely used in the field of packaging materials, and these composite films are produced by bonding various plastic films and metal foil, and others by using an adhesive. As the adhesive for lamination, an organic solvent-based two-component curable adhesive comprising a mixture of an organic polyisocyanate compound and a polyester polyol, a polyether polyol, a polyurethane polyol or any mixture of these polymers has been used.
However, in recent years, for improving working environment and regulation of the use of solvents, the organic solvent-based adhesives have been replaced gradually with solvent-free adhesives in the production of composite laminated films. As such solvent-free adhesives for lamination, an adhesive composition comprising a polyol component and a polyisocyanate component has been used.
Composite laminated films using solvent-free adhesive compositions are produced with use of a laminator (for a solvent-free adhesive). A process for producing composite laminated films with use of the laminator is illustrated with referring to FIG. 1.
A polyol component and a polyisocyanate component are usually supplied from tanks 1 and 2, respectively, and the components are mixed by a mixer 3 before the components reach at coating part (area) of a laminator. The resultant adhesive 4 is supplied between a doctor roll 5 and a metering roll 6 which are rotated in the opposite direction each other. The adhesive 4 is transferred from the metering roll 6 to a coating roll 7, and is coated on a film 9 which is supplied between the coating roll 7 and a impression roll 8. The film 9 on which the adhesive is coated, and the other film 10 are supplied between a laminating roll 11 and a nip roll 12, to bond or adhere the coating surface of the film 9 with the film 10, and then rolled up by a winding unit to produce a composite laminated film 13 having two layers structure. Furthermore, if necessary, a composite laminated film composed of three or more layers may be sometimes produced in the same manner. The respective shapes of coating parts of the doctor roll 5, the metering roll 6 and the coating roll 7 and the impression roll 8 are different depending on equipment, and this figure shows just one embodiment thereof.
The conventional solvent-free adhesives, depending on the laminating conditions, is liable to cause deterioration (detraction) of the external appearance due to unevenness of coating surface caused by forcibly peeling the coating layer on the film 9 from the coating roll 7 or non-uniformity of thickness of the coated adhesive. In particular, there has propensity to cause deterioration of the external appearance when laminating at high speed and laminating a film having high rigidity such as polyethylene terephthalate film and others. Thus, a low coating speed (e.g., 100 m/minute or less of a lamination speed) is required, and causes reduction in working efficiency.
Moreover, in the case of lamination with the conventional solvent-free adhesives by a laminator, in most cases, foam comes to be contained in the adhesive accumulated between the doctor roll 5 and the metering roll 6, the foam is transferred to the coating layer as such on the film, and the film is laminated. As a result, in most cases, the initial external appearance of the composite laminated film makes worse.
Moreover, usually, for accelerating reaction of an isocyanate group with a hydroxyl group and improving conformability of the adhesive to the film after lamination as well, the composite laminated film often allows to warm at 30 to 60xc2x0 C. for one or more days (hereinafter, referring as aging (or aging step)). However, when the external appearance of the film at the time immediately after lamination deteriorates and remarkably differs from that of the film at the time after aging step, quality (appearance) of the composite laminated film as the final product obtained from aging step can not be evaluated (imaged) immediately after laminating step. Furthermore, as a lamination speed is faster, large foam generated in the film remains intact. Part of the foam remains without disappearance even after aging step, as a result, deterioration of the external appearance sometimes occurs in the film.
On the other hand, a coating amount and an initial adhesive strength (or adhesive properties) depend on the viscosity of the solvent-free adhesive. Thus, for overcoming the above-mentioned problems, if the viscosity of the adhesive allows lower, it becomes difficult to keep an amount of coating and the initial adhesive strength. As a result, there has propensity to deteriorate the external appearance due to blur and tunneling (embossment) to the composite laminated film, and there has propensity to delaminate if three or more layer are laminated.
Japanese Patent Application Laid-open No. 181393/1999 (JP-11-181393A) discloses a solvent-free two-component curable adhesive composition comprising a hydroxyl group-containing compound such as a crystalline polymer polyol, and an isocyanate-containing compound, wherein a mixture of both compounds is solid or semisolid state. Even if the adhesive composition is used, however, when a film having high rigidity is laminated at high speed, the external appearance of the composite laminated film is remarkably deteriorated.
Therefore, it is an object of the present invention to provide a solvent-free curable adhesive composition (a solvent-free two-component curable adhesive composition) capable of producing a composite laminated film having the superior external appearance simply and efficiently, and a process of lamination using such a adhesive composition.
It is another object of the present invention to provide a solvent-free two-component curable adhesive composition capable of having an improved initial adhesive strength, and a process of lamination using such a adhesive composition.
It is further another object of the present invention to provide a solvent-free two-component curable adhesive composition and a process of lamination capable of producing a composite laminated film having the good external appearance at the time both immediately after lamination and after aging step, even when laminating at high speed or laminating with a film having high rigidity such as polyethylene terephthalate.
The inventors of the present invention made intensive studies to achieve the above objects, and finally found that use of a component containing a specific crystalline polyol component at certain ratio as a polyol component and/or a polyisocyanate component enables to produce a composite laminated film having high initial adhesive strength and having superior appearance even when laminated at high speed simply. The present invention was accomplished based on the above findings.
That is, the solvent-free two-component curable adhesive composition of the present invention comprises (A) a polyol component and (B) a polyisocyanate component, wherein at least one component of the components (A) and (B) comprises at least one polyol component having crystallinity at room temperature and selected from the group consisting of a polyester polyol, a polyether polyol, a polycarbonate polyol and a polyurethane polyol, and an amount of the crystalline polyol component is 3 to 50% by weight (particularly, 3 to 45% by weight) relative to the total weight of the components (A) and (B). The polyol component may be crystalline, or the crystalline polyol component may be contained in the polyol component and/or the isocyanate component as a constructive unit or segment. The composition has an initial viscosity of about 100 to 1,500 mPaxc2x7s (e.g., about 200 to 1,500 mPaxc2x7s) at 70xc2x0 C. immediately after the components (A) and (B) are mixed together, and an increasing ratio of the viscosity after the composition is stood at 70xc2x0 C. for 10 minutes to the initial viscosity of 120% or less (e.g., 110% or less). Moreover, the concentration of aromatic rings (as a constituting unit) in the total weight of the components (A) and (B) may be 0.2 to 2.8 mmol/g (particularly, 0.4 to 2.6 mmol/g).
In the composition, the component (A) may comprise polyester polyol obtainable from a polybasic acid (e.g., an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid) and a polyol component (e.g., an alkanepolyol and a polyether polyol). A number average molecular weight of the component (A) may be about 400 to 5,000 (for example, about 400 to 4,000). The component (A) may further comprise an alkanepolyol and a polyether polyol, and others. The component (B) has a plurality of terminal isocyanate groups, and may be the followings (B1), (B2), and others: (B1) a reaction product of a polyol component (e.g., an alkanepolyol, a polyester polyol, a polyether polyol, a polycarbonate polyol and a polyurethane polyol) and a polyisocyanate [e.g., an araliphatic diisocyanate and a biphenyl-series diisocyanate]; and (B2) apolyisocyanate (e.g., a aliphatic diisocyanate) derivative.
The crystalline polyol component may be composed of at least one member selected from the followings (i) and (ii): (i) a polyester polyol obtainable from at least one member selected from the group consisting of an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid, and at least one polyol component selected from the group consisting of an alkanepolyol and a polyether polyol; and (ii) a polyether polyol. A number average molecular weight of the crystalline polyol component may be about 400 to 4,000. Moreover, the above-mentioned composition may comprise an antifoaming agent and/or a foam stabilizer, an adhesion improving agent (e.g., a coupling agent, an oxygen acid of phosphorus, and an epoxy compound or resin), and others.
A composite film, without deterioration of the external appearance, can be obtainable with use of the composition, even if the film is laminated at high speed (e.g., 100 m/minute or more of a lamination speed). Moreover, a high quality composite film can be obtainable with use of the composition, even when high rigidity films (particularly, a plurality of films including a polyalkylene arylate-series resin film) are laminated.
The present invention also includes a process for laminating a plurality of films with the use of the composition.
The present invention further includes use of the composition for producing a laminated film (laminate).